Conventionally, such a system has been required that identifies articles and persons in fields such as management of distribution, management of products at plants, management of administration at gates in ski areas, and automatic ticket gates.
A contactless communication system thus has been proposed that provides a memory unit (a data carrier) having memory to a object to be identified and writes necessary information to the data carrier externally through data transfer so that the information can be read as required.
As shown in FIG. 9A, in a contactless communication system, multiple data carriers DC1 to DC4 may enter the communication area SE of a reader/writer R/W. Even in such a case, each data carrier need to be identified for normal data communication.
In a conventional system, each data carrier is given a unique identification number in advance, and a reader/writer R/W sends commands for getting identification numbers and receives data on identification numbers from the data carriers DC1 to DC4 in order to identify data carriers DC1 to DC4.
At this time, if multiple data carriers are present in a communication area and data carriers DC1 to DC4 simultaneously respond, the responses may not be conveyed to the reader/writer R/W normally due to interference.
Accordingly, as shown in FIG. 9B, there is a known identification system in which, after receiving the command, each of the data carriers DC1 to DC4 responds after a time period that is defined as a multiple of a certain time period as a unit so that responses from data carriers DC1 to DC4 would not occur at a time.
The conventional method of identifying multiple data carriers has adopted a system which sends back all bits of identification information held by a data carrier in response to a request for response from a reader/writer. This system, however, has such a defect that processing for identification is time consuming since all bits of data is sent back, although all bits of data for identification information is not required to identify each data carrier if the number of bits for identification information is large enough compared to the number of data carriers to be identified that exist around a reader/writer.
In addition, the above-mentioned system in which, upon reception of a command for requesting a response, a data carrier will respond after a time period that is defined as a multiple of a certain time as a unit has a defect that its processing is inefficient since an extra time of one frame is required at the end to confirm the completion of identification.
An object of the present invention is to provide a contactless communication system that can reduce the time required for completing identification of all of multiple data carriers that exist around a reader/writer and attempt the speed-up of its processing.